Research On Oil And Water Two-Phase Unsteady Seepage In Carbonate Reservoir

With the increasing of energy demand and the deepening of oil and gas exploration in the world,the development of carbonate reservoir has become the key research direction of reservoir engineers and scholars.According to incomplete statistics,carbonate reservoirs of oil and gas reserves accounted for more than 50% of total reserves,and the oil and gas production accounts for more than 60% of the total production in the world’s 236 major oil fields;it has the characteristics of wide distribution,multi type,large reserves and high productivity.However,the carbonate reservoir has the characteristics of the deep burial,the long geological age and the long term diagenesis and transformation,hence it has the fracture,karst,fault and other macro discontinuous surface,which results in the diversity of reservoir space of this reservoir;the relationship between oil and water and fluid flow in reservoir is complex,the decline of production is fast,the water-free oil production period is short,and the oil and water flow occurred earlier in the reservoir.Therefore,the theory of oil-water two-phase unstable seepage in the fracture-vug type carbonate reservoir is carried out,and the effects of various formation parameters,fluid parameters and fracturing parameters on the seepage of fracture-vug type carbonate reservoirs are analyzed.Reservoir seepage law,which is of great significance to the systematic study of fracture-vug type carbonate reservoirs.In this study,based on the extensive investigation of the domestic and foreign research results,and the research results of geological characteristics of carbonate reservoirs in China,the oil and water two-phase unsteady seepage theory in fractured vuggy carbonate reservoir was researched by using seepage mechanics theory,many kinds of modern mathematical methods and computer programming technology.The main research work of this study is as follows:(1)According to literature,geological characteristics and reservoir characteristics of fractured vuggy carbonate reservoir are analysed,and some kinds of oil and water two phase flow models of fractured vuggy carbonate reservoir are proposed.(2)Based on the study of multi-scale spatial characteristics of carbonate reservoir,the pseudo steady state and unsteady state models for the basic seepage flow of oil and water two-phase flow in porous-fracture and porous-fracture-vug systems are proposed.(3)According to the above mentioned physical model of oil-water two-phase flow in fractured vuggy carbonate reservoirs with various percolation models,the formula for calculating the pressure response of a continuous point source in the fractured vuggy carbonate reservoir under the conditions of top and bottom impermeable and different lateral boundaries is proposed.(4)Based on the formula for calculating the pressure response of a continuous point source in the fractured vuggy carbonate reservoir,the formula for calculating bottomhole pressure and productivity of many kinds of well under the conditions of the infinite outer boundary and the circular boundary are proposed,where the well types include the vertical well(completely and partially perforated),fractured vertical well(infinite conductivity and finite conductivity),horizontal well and multi-fractured horizontal well(infinite conductivity and finite conductivity).(5)The well test curves and well production decline curves for different types of well,reservoir,and boundary are drawn,and the characteristics of the curves and the corresponding flow in the formation are also analysed.(6)The applicability of the models in this study are verified by the measured data of oil wells in carbonate reservoirs.Based on this study,the formula for calculating bottomhole pressure and productivity of many kinds of well under the conditions of the infinite outer boundary and the circular boundary are proposed,the effects of various formation parameters,fluid parameters and fracturing parameters on the seepage of fracture-vug type carbonate reservoirs are analyzed,a set of dynamic analysis method and technology of single well production for oil and water two-phase flow in fractured vuggy carbonate reservoir is developed,the understanding of fluid flow in matrix,fracture and vug are deeper,and the theory of unstable seepage in carbonate reservoir is developed.It provides a theoretical basis for the efficient development of such reservoirs.